1. Technical Field
The present invention relates to a data address mark for a hard disk drive and, more particularly, relates to a method for forming and processing data address mark for hard disk drive in order to improve production yield.
2. Related Art
Hard disk drive is widely used as an auxiliary memory device of a computer system because it can access a large amount of data at high speed. Generally, hard disk drive utilizes a recording form based on constant-track capacity to record and reproduce data to and from a magnetic disk. In this recording form, the hard disk drive rotates at a constant velocity, and information capacity per track of inner tracks of a magnetic disk is the same as that of outer tracks. However, information recording density of the outer tracks is lower than that of the inner tracks because the outer track is substantially larger than the inner tracks. Consequently, the storage efficiency of the magnetic disk is minimal.
One popular technique to increase the information recording density of a magnetic disk is a recording type of constant linear density (CLD) or zone-bit recording. In the constant linear density recording form, all tracks including inner and outer tracks contain the same information density in order to improve the information capacity of the magnetic disk. Moreover, an information recording area of the magnetic disk is split into a plurality of zones so as to have constant recording density in a radial direction from the center of the magnetic disk. The number of data sectors is differently assigned to the tracks of each split zone. That is, the tracks of an outer zone have the number of the data sectors more than the tracks of an inner zone. The data sector designates a unit area for accessing data on the magnetic disk by the hard disk drive and has the same size, 512 bytes for example, irrespective of the position of the magnetic disk. If an embedded sector servo system as disclosed, for example, in U.S. Pat. No. 5,210,660 for Sectored Servo Independent Of Data Architecture issued to Hetzler, U.S. Pat. No. 5,384,671 for PRML Sampled Data Channel Synchronous Servo Detector issued to Fisher, U.S. Pat. No. 5,420,730 for Servo Data Recovery Circuit For Disk Drive Having Digital Embedded Sector Servo issued to Moon et al., U.S. Pat. No. 5,475,540 for Magnetic Data Storage Disk Drive With Data Block Sequencing By Using ID Fields After Embedded Servo Sectors issued to Gold, is used to provide position information of a transducer (head), one data sector may split into two segments according to each area on the magnetic disk. In such an embedded sector servo system, each data track is divided into a servo information area and a data information area which are alternatively provided in a radial direction of the magnetic disk. The servo information area is an area into which servo information is written and provides a servo sector. The data information area is an area into which actual data information is written and provides a data sector.
Typical data sector includes a plurality of identification (ID) regions, data regions and PAD regions serving as intersector gaps therebetween. Commonly, the ID region includes an ID preamble, an ID address mark (AM), a cyclic redundancy check code (CRC) and an ID postamble. The data region includes a data address mark (AM), data and an error correction code (ECC). Generally, in order to read information of the ID region and the data region of the respective data section, the HDD must be synchronized with a clock frequency previously written on the magnetic disk by using the ID sync and data sync. In practice however, the ID preamble requires many bytes that are restrictive for high density HDD application.
Another technique to improve information recording density in hard disk drives in recent years is known as a recording type of headerless sector format as disclosed, for example, in U.S. Pat. No. 5,500,848 for Sector Servo Data Recording Disk Having Data Regions Without Identification (ID) Fields issued to Best et al, U.S. Pat. No. 5,523,903 for Sector Architecture For Fixed Block Disk Drive issued to Hetzler et al., U.S. Pat. No. 5,581,418 for Magnetic Disk Drive Unit Capable Of Determining Data Region Position Of Data Region That Does Not Include Position Identification Data issued to Hasebe, U.S. Pat. No. 5,627,695 for System And Method For Generating Unique Sector Identifiers For An Identificationless Disk Format issued to Prins, and U.S. Patent No. 5,589,998 for Cylinder Address Storage In Multiple Servo Sectors Of A Track issued to Yu. In Best et al. '848, for example, a fixed block architecture sector format that includes information encoded in the servo region of a sector to enable a data recording head to locate and identify data sector for read and write operations without the need of an ID region. Similarly, Hetzer et al. '903 and Hasebe '418 each discloses a sector architecture that further includes information contained in electronic storage to enable the data recording head to locate and identify data sectors for read and write operations without using data ID fields. Likewise, Prins '695 and Yu '998 also disclose a disk drive system for determining sector ID of a data sector on a disk without using ID fields in order to maximize disk capacity.
Generally, servo sector of the HDD using a headerless servo format includes a preamble region for synchronizing with a system clock, a servo address mark (SAM) region for recording a reference pattern for producing various servo timing signals, an index (IDX) region for supplying a single rotation information of the disks, a sector number region for recording a servo sector number, a head number region for recording the head number, a gray code region for recording track information, a servo burst region for the on-track control of the heads and a postamble region. Common servo address mark (SAM) detection scheme maybe disclosed, for example, in U.S. Pat. No. 5,231,545 for Fault Tolerant RLL Data Sector Address Mark Decoder issued to Gold, U.S. Pat. No. 5,442,499 for Method Of Detecting Sector Servo Information In A Disk System issued to Emori, and U.S. Pat. No. 5,544,135 for Fault Tolerant Servo Address Mark For Disk Drive issued to Akin, Jr. et al.
Meanwhile, data sector of HDD using a headerless servo format includes a data preamble region, a data address mark, data, an error correction code (ECC) and a data postamble. The data address mark informs that the data is started and provides necessary synchronization when data is recorded on or read from the magnetic disk. Data is the actual digital information stored in the magnetic disk. ECC is an error detecting code for detecting and correcting an error of the data. The data postamble provides a necessary timing margin after reading the data. Since the ID post amble is adjacent to the data preamble, and the data postamble is adjacent to the ID preamble, they are mixedly used.
In contemporary HDD using the headerless recording format, if there is occurrence of a defect in a data area, damaged data can be restored by using the ECC. If there is occurrence of a defect in a data address mark area, however, it is difficult if not impossible to restore the damaged data address mark. As a result, since the data address mark is not detected, data positioned at a rear area following the data address mark cannot be normally accessed. Moreover, if such a data field is over tolerance limits, the HDD needs to be repaired or discarded, thereby losing valuable operational time and financial resources.